Boys grow first and then change their voices, the child’s growth and development is such a process, the height of 50cm at birth, the first year can grow 25cm, 2-12 years old children’s growth formula is (age x 7) + 75. puberty is 11-20 years old, puberty can be divided into three stages, the first stage is before and after the change of voice that is, before the appearance of the second sex characteristics, the second stage is the appearance of the second sex characteristics, the second stage is the appearance of the second sex characteristics, the third stage is the latter three years. The third stage is the last three years. Each stage is about three years long, and voice change usually occurs during the second stage, around the age of 14.